Vertical microbolometer contact systems and methods

ABSTRACT

Systems and methods are directed to vertical legs for an infrared detector. For example, an infrared imaging device may include a microbolometer array in which each microbolometer includes a bridge and a vertical leg structure that couples the bridge to a substrate such as a readout integrated circuit. The vertical leg structure may run along a path that is parallel to a plane defined by the bridge and may be oriented perpendicularly to the plane. The path may be disposed within, below, or above the plane defined by the bridge.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/396,100 filed Dec. 30, 2016 and entitled “VERTICAL MICROBOLOMETERCONTACT SYSTEMS AND METHODS,” which is a continuation of InternationalPatent Application No. PCT/US2015/039138 filed Jul. 2, 2015 and entitled“VERTICAL MICROBOLOMETER CONTACT SYSTEMS AND METHODS,” which in turnclaims priority to and the benefit of U.S. Provisional PatentApplication No. 62/020,747 filed on Jul. 3, 2014 and entitled “VERTICALMICROBOLOMETER CONTACT SYSTEMS AND METHODS,” the contents all of whichare hereby incorporated by reference in their entirety.

TECHNICAL FIELD

One or more embodiments of the invention relate generally to infraredcameras and, more particularly, to microbolometer contact systems andmethods, such as vertical leg contacts for microbolometer focal planearrays.

BACKGROUND

A microbolometer is an example of a type of infrared detector that maybe used within an infrared imaging device (e.g., an infrared camera).For example, the microbolometer is typically fabricated on a monolithicsilicon substrate to form an infrared (image) detector array, with eachmicrobolometer of the infrared detector array functioning as a pixel toproduce a two-dimensional image. The change in resistance of eachmicrobolometer is translated into a time-multiplexed electrical signalby circuitry known as the read out integrated circuit (ROIC). Thecombination of the ROIC and the infrared detector array (e.g.,microbolometer array) is commonly known as a focal plane array (FPA) orinfrared FPA (IRFPA). Additional details regarding FPAs andmicrobolometers may be found, for example, in U.S. Pat. Nos. 5,756,999,6,028,309, 6,812,465, and 7,034,301, which are herein incorporated byreference in their entirety.

Each microbolometer in the array is generally coupled to one or morecontacts that extend vertically from the array down to the ROIC. Thecontacts can be used for providing a reference voltage for themicrobolometer and/or a signal path from the microbolometer to the ROIC.Microbolometers often include a light-sensitive portion formed fromresistive material suspended on a bridge, with the resistive materialcoupled to its contacts via legs that run from the bridge to thecontacts. The legs attach to resistive material through a resistivematerial contact.

One of the challenges in designing efficient microbolometers isincreasing the ratio of the light-sensitive area or the active pixelarea to the total area of the array, sometimes referred to as the fillfactor of the array. Leg supports for each microbolometer can occupy asignificant portion of the array area and can therefore limit the fillfactor of the array. It would therefore be desirable to reduce theamount of area occupied by the legs. However, in order to maintaindevice performance, the width and length of each leg support shouldscale with the area of each pixel. It can therefore be difficult toreduce the leg area and increase the fill factor. As a result, there isa need for improved techniques for implementing leg supports, such asfor microbolometer-based focal plane arrays.

SUMMARY

Systems and methods are disclosed, in accordance with one or moreembodiments, which are directed to microbolometer legs for an infrareddetector. For example, in accordance with an embodiment of theinvention, vertical legs are disclosed, such as for infrared detectorswithin a focal plane array, that may be more area efficient as comparedto conventional legs that extend horizontally substantially in planewith the infrared detector. For one or more embodiments, the leg systemsand methods disclosed herein may provide certain advantages overconventional leg approaches, especially as semiconductor processingtechnologies transition to smaller dimensions.

In accordance with one embodiment, an infrared imaging device includesan array of microbolometers each having a bridge that is coupled to acontact by at least one vertical bolometer leg. The legs and bridges ofthe microbolometer array may be suspended above a readout integratedcircuit for the microbolometer array. The vertical bolometer legs may beformed using spacer deposition and etch processing operations that format least portions of the vertical bolometer legs on the sidewalls of anopening in a sacrificial layer that is then removed to release thebolometer legs.

According to various embodiments, a vertical bolometer leg may run alonga path that is disposed in a plane that is parallel to a plane definedby the bridge of the microbolometer and/or a plane that is defined by asurface of a substrate of the device such as a readout integratedcircuit substrate and may have an extended dimension that extends in adirection that is perpendicular to the plane of the path, the substratesurface, and/or the plane of the bridge. In this way, the area of thebolometer leg that would otherwise occupy a relatively larger fractionof the surface area of the microbolometer array can be reduced withoutreducing the area of the bolometer leg.

According to various embodiments, the leg structure may or may not beencapsulated in an insulating layer such as a silicon dioxide or asilicon nitride. The leg structure may be formed from multiple layers ofinsulating material to optimize performance. A leg conductive layer maybe fully or partially encapsulated with an insulation layer, or may befree of any insulation layer. The leg conductive layer may be ahomogeneous film of a single material type or a multilayer conductivelayer formed from, for example, several depositions.

The scope of the invention is defined by the claims, which areincorporated into this Summary by reference. A more completeunderstanding of embodiments of the invention will be afforded to thoseskilled in the art, as well as a realization of additional advantagesthereof, by a consideration of the following detailed description of oneor more embodiments. Reference will be made to the appended sheets ofdrawings that will first be described briefly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram illustrating an infrared camera inaccordance with one or more embodiments.

FIG. 2 shows a block diagram illustrating an implementation example foran infrared camera in accordance with one or more embodiments.

FIG. 3 shows a physical layout diagram of a microbolometer of amicrobolometer array having vertical legs in accordance with anembodiment.

FIGS. 4A and 4B show a top view and a cross-sectional side viewrespectively of a conventional horizontal leg for a microbolometer.

FIGS. 5A and 5B show a top view and a cross-sectional side viewrespectively of a vertical leg such as for a leg for coupling aninfrared detector element to a contact, in accordance with anembodiment.

FIGS. 6A through 6F illustrate a processing overview for manufacturing avertical leg, such as for the vertical legs of FIG. 3, in accordancewith an embodiment.

FIGS. 7A through 7F illustrate another processing overview formanufacturing a vertical leg, such as for the vertical legs of FIG. 3,in accordance with an embodiment.

FIGS. 8A through 8C illustrate a yet another processing overview formanufacturing a vertical leg, such as for the vertical legs of FIG. 3,in accordance with an embodiment.

FIG. 9 shows a cross-sectional side view, in the vicinity of a verticalcontact between an infrared detector array and a readout integratedcircuit, of a portion of a focal plane array having vertical legs thatare formed below a surface of the array, in accordance with anembodiment.

FIG. 10 shows a cross-sectional side view, in the vicinity of a sensorof the array, of a portion of a focal plane array having vertical legsthat are formed below a surface of the array, in accordance with anembodiment.

FIG. 11 shows a cross-sectional side view, in the vicinity of a verticalcontact between an infrared detector array and a readout integratedcircuit, of a portion of a focal plane array having vertical legs thatare formed below a surface of the array, in accordance with anembodiment.

FIG. 12 shows a cross-sectional side view, in the vicinity of a sensorof the array, of a portion of a focal plane array having vertical legsthat are formed below a surface of the array, in accordance with anembodiment.

FIGS. 13A through 13Q show various arrangements of a vertical leg, suchas for the vertical legs of FIGS. 5A and 5B, in accordance with variousembodiments.

FIG. 14 shows a cross-sectional side view, in the vicinity of a verticalcontact between an infrared detector array and a readout integratedcircuit, of a portion of a focal plane array having vertical legs formedat or above a surface of the array, in accordance with an embodiment.

FIG. 15 shows a cross-sectional side view, in the vicinity of a sensorof the array, of a portion of a focal plane array having vertical legsformed above a surface of the array, in accordance with an embodiment.

FIG. 16 shows a top view of a bend portion of a vertical leg, such asfor the vertical legs of FIG. 3 in the vicinity of a bend in thevertical leg, in accordance with an embodiment.

FIG. 17 shows a cross-sectional view of an example arrangement of thevertical leg of FIG. 16, in accordance with an embodiment.

FIG. 18 shows a cross-sectional view of another example arrangement ofthe vertical leg of FIG. 16, in accordance with an embodiment.

FIG. 19 shows a cross-sectional view of a portion of a focal plane arrayhaving legs, such as legs for an infrared detector, that are formed atleast partially beneath a bridge portion of the infrared detector, inaccordance with an embodiment.

FIG. 20 illustrates a flow diagram for manufacturing a vertical leg,such as for the vertical legs of FIG. 3, in accordance with anembodiment.

FIG. 21 illustrates another flow diagram for manufacturing a verticalleg, such as for the vertical legs of FIG. 3, in accordance with anembodiment.

FIG. 22 illustrates yet another flow diagram for manufacturing avertical leg, such as for the vertical legs of FIG. 3, in accordancewith an embodiment.

FIGS. 23A through 23F illustrate a processing overview for manufacturinga vertical leg, such as for the vertical legs of FIG. 3 using an etchstop layer, in accordance with an embodiment.

FIG. 24 shows a cross-sectional view of a portion of a focal plane arrayhaving legs, such as legs for an infrared detector, that are formed atleast partially beneath a bridge portion of the infrared detector, inaccordance with an embodiment.

FIG. 25 illustrates a flow diagram for manufacturing a focal plane arrayhaving legs, such as legs for an infrared detector, that are formed atleast partially beneath a bridge portion of the infrared detector, inaccordance with an embodiment.

Embodiments of the invention and their advantages are best understood byreferring to the detailed description that follows. It should beappreciated that like reference numerals are used to identify likeelements illustrated in one or more of the figures.

DETAILED DESCRIPTION

Systems and methods are disclosed herein to provide vertically orientedlegs for an infrared detector, in accordance with one or moreembodiments. For example, in accordance with an embodiment, verticalbolometer legs are disclosed, such as for microbolometers within a focalplane array. As an implementation example, FIG. 1 shows a block diagramillustrating a system 100 (e.g., an infrared camera, including any typeof infrared imaging system) for capturing images and processing inaccordance with one or more embodiments. System 100 comprises, in oneimplementation, an image capture component 102, a processing component104, a control component 106, a memory component 108, and a displaycomponent 110. Optionally, system 100 may include a sensing component112.

System 100 may represent, for example, an infrared imaging device, suchas an infrared camera, to capture and process images, such as videoimages of a scene 101. The system 100 may represent any type of infraredcamera that employs infrared detectors having contacts, which may beimplemented as disclosed herein. System 100 may comprise a portabledevice and may be incorporated, e.g., into a vehicle (e.g., anautomobile or other type of land-based vehicle, an aircraft, or aspacecraft) or a non-mobile installation requiring infrared images to bestored and/or displayed or may comprise a distributed networked system(e.g., processing component 104 distant from and controlling imagecapture component 102 via the network).

In various embodiments, processing component 104 may comprise any typeof a processor or a logic device (e.g., a programmable logic device(PLD) configured to perform processing functions). Processing component104 may be adapted to interface and communicate with components 102,106, 108, and 110 to perform method and processing steps and/oroperations, such as for example, controlling biasing and other functions(e.g., values for elements such as variable resistors and currentsources, switch settings for biasing and timing, and other parameters)along with other conventional system processing functions as would beunderstood by one skilled in the art.

Memory component 108 comprises, in one embodiment, one or more memorydevices adapted to store data and information, including for exampleinfrared data and information. Memory device 108 may comprise one ormore various types of memory devices including volatile and non-volatilememory devices, including computer-readable medium (portable or fixed).Processing component 104 may be adapted to execute software stored inmemory component 108 so as to perform method and process steps and/oroperations described herein.

Image capture component 102 comprises, in one embodiment, one or moreinfrared sensors (e.g., any type of multi-pixel infrared detector, suchas a focal plane array having one or more vertical legs as disclosedherein) for capturing infrared image data (e.g., still image data and/orvideo data) representative of an image, such as scene 101. In oneimplementation, the infrared sensors of image capture component 102provide for representing (e.g., converting) the captured image data asdigital data (e.g., via an analog-to-digital converter included as partof the infrared sensor or separate from the infrared sensor as part ofsystem 100). In one or more embodiments, image capture component 102 mayfurther represent or include a lens, a shutter, and/or other associatedcomponents along with the vacuum package assembly for capturing infraredimage data. Image capture component 102 may further include temperaturesensors (or temperature sensors may be distributed within system 100) toprovide temperature information to processing component 104 as tooperating temperature of image capture component 102.

In one aspect, the infrared image data (e.g., infrared video data) maycomprise non-uniform data (e.g., real image data) of an image, such asscene 101. Processing component 104 may be adapted to process theinfrared image data (e.g., to provide processed image data), store theinfrared image data in memory component 108, and/or retrieve storedinfrared image data from memory component 108. For example, processingcomponent 104 may be adapted to process infrared image data stored inmemory component 108 to provide processed image data and information(e.g., captured and/or processed infrared image data).

Control component 106 comprises, in one embodiment, a user input and/orinterface device, such as a rotatable knob (e.g., potentiometer), pushbuttons, slide bar, keyboard, etc., that is adapted to generate a userinput control signal. Processing component 104 may be adapted to sensecontrol input signals from a user via control component 106 and respondto any sensed control input signals received therefrom. Processingcomponent 104 may be adapted to interpret such a control input signal asa parameter value, as generally understood by one skilled in the art. Inone embodiment, control component 106 may comprise a control unit (e.g.,a wired or wireless handheld control unit) having push buttons adaptedto interface with a user and receive user input control values. In oneimplementation, the push buttons of the control unit may be used tocontrol various functions of the system 100, such as autofocus, menuenable and selection, field of view, brightness, contrast, noisefiltering, high pass filtering, low pass filtering, and/or various otherfeatures as understood by one skilled in the art.

Display component 110 comprises, in one embodiment, an image displaydevice (e.g., a liquid crystal display (LCD) or various other types ofgenerally known video displays or monitors). Processing component 104may be adapted to display image data and information on the displaycomponent 110. Processing component 104 may be adapted to retrieve imagedata and information from memory component 108 and display any retrievedimage data and information on display component 110. Display component110 may comprise display electronics, which may be utilized byprocessing component 104 to display image data and information (e.g.,infrared images). Display component 110 may be adapted to receive imagedata and information directly from image capture component 102 via theprocessing component 104, or the image data and information may betransferred from memory component 108 via processing component 104.

Optional sensing component 112 comprises, in one embodiment, one or moresensors of various types, depending on the application or implementationrequirements, as would be understood by one skilled in the art. Thesensors of optional sensing component 112 provide data and/orinformation to at least processing component 104. In one aspect,processing component 104 may be adapted to communicate with sensingcomponent 112 (e.g., by receiving sensor information from sensingcomponent 112) and with image capture component 102 (e.g., by receivingdata and information from image capture component 102 and providingand/or receiving command, control, and/or other information to and/orfrom one or more other components of system 100).

In various implementations, sensing component 112 may provideinformation regarding environmental conditions, such as outsidetemperature, lighting conditions (e.g., day, night, dusk, and/or dawn),humidity level, specific weather conditions (e.g., sun, rain, and/orsnow), distance (e.g., laser rangefinder), and/or whether a tunnel orother type of enclosure has been entered or exited. Sensing component112 may represent conventional sensors as generally known by one skilledin the art for monitoring various conditions (e.g., environmentalconditions) that may have an effect (e.g., on the image appearance) onthe data provided by image capture component 102.

In some implementations, optional sensing component 112 (e.g., one ormore of sensors) may comprise devices that relay information toprocessing component 104 via wired and/or wireless communication. Forexample, optional sensing component 112 may be adapted to receiveinformation from a satellite, through a local broadcast (e.g., radiofrequency (RF)) transmission, through a mobile or cellular networkand/or through information beacons in an infrastructure (e.g., atransportation or highway information beacon infrastructure), or variousother wired and/or wireless techniques.

In various embodiments, components of system 100 may be combined and/orimplemented or not, as desired or depending on the application orrequirements, with system 100 representing various functional blocks ofa related system. In one example, processing component 104 may becombined with memory component 108, image capture component 102, displaycomponent 110, and/or optional sensing component 112. In anotherexample, processing component 104 may be combined with image capturecomponent 102 with only certain functions of processing component 104performed by circuitry (e.g., a processor, a microprocessor, a logicdevice, a microcontroller, etc.) within image capture component 102.Furthermore, various components of system 100 may be remote from eachother (e.g., image capture component 102 may comprise a remote sensorwith processing component 104, etc. representing a computer that may ormay not be in communication with image capture component 102).

FIG. 2 shows a block diagram illustrating a specific implementationexample for an infrared camera 200 in accordance with one or moreembodiments. Infrared camera 200 may represent a specific implementationof system 100 (FIG. 1), as would be understood by one skilled in theart.

Infrared camera 200 (e.g., a microbolometer readout integrated circuitwith bias-correction circuitry and interface system electronics)includes a readout integrated circuit (ROIC) 202, which may include themicrobolometer unit cell array having one or more contacts coupled tomicrobolometer bridges via vertical legs as disclosed herein, controlcircuitry, timing circuitry, bias circuitry, row and column addressingcircuitry, column amplifiers, and associated electronics to provideoutput signals that are digitized by an analog-to-digital (A/D)converter 204. The A/D converter 204 may be located as part of orseparate from ROIC 202.

The output signals from A/D converter 204 are adjusted by anon-uniformity correction circuit (NUC) 206, which applies temperaturedependent compensation as would be understood by one skilled in the art.After processing by NUC 206, the output signals are stored in a framememory 208. The data in frame memory 208 is then available to imagedisplay electronics 210 and a data processor 214, which may also have adata processor memory 212. A timing generator 216 provides systemtiming.

Data processor 214 generates bias-correction data words, which areloaded into a correction coefficient memory 218. A data register loadcircuit 220 provides the interface to load the correction data into ROIC202. In this fashion, variable circuitry such as variable resistors,digital-to-analog converters, biasing circuitry, which control voltagelevels, biasing, frame timing, circuit element values, etc., arecontrolled by data processor 214 so that the output signals from ROIC202 are uniform over a wide temperature range.

It should be understood that various functional blocks of infraredcamera 200 may be combined and various functional blocks may also not benecessary, depending upon a specific application and specificrequirements. For example, data processor 214 may perform variousfunctions of NUC 206, while various memory blocks, such as correctioncoefficient memory 218 and frame memory 208, may be combined as desired.

FIG. 3 shows a physical layout diagram of a microbolometer 300 inaccordance with an embodiment of the invention. Microbolometer 300includes a bridge portion 302 having a light sensor 304 and bridgecontacts 306 that couple sensor 304 to a first end of legs 308. Legs 308each couple sensor 304 to one of contacts 310.

Each contact 310 may couple one or more associated microbolometers 300to associated readout circuitry of a readout integrated circuit (ROIC,not shown). For example, a first contact 310 may be used to provide areference or bias voltage to the microbolometer and a second contact 310may be used to a signal path from the microbolometer to the ROIC bywhich signals corresponding to infrared light absorbed by themicrobolometer can be readout. Further descriptions of ROIC andmicrobolometer circuits may be found in U.S. Pat. No. 6,028,309, whichis incorporated by reference in its entirety herein for all purposes.

Sensor 304 may be arranged to convert incident light such as infraredlight into detectable electrical signals based on changes in electricalproperties of the sensor (e.g., changes in resistivity) due to changesin temperature of the sensor when the light is incident. According to anembodiment, sensor 304 may include a resistive material, which may beformed of a high temperature coefficient of resistivity (TCR) material(e.g., vanadium oxide (VOx) or amorphous silicon). The resistivematerial may be suspended above the ROIC on bridge 302 and coupled toits contacts 310 via legs 308.

According to various embodiments, each contact 310 may be attached to aportion of a leg 308 that bends downward toward the ROIC (e.g., contact310 may be formed on a substrate such as the ROIC and leg 308 mayinclude a portion that runs at a non-perpendicular angle to thesubstrate from a first height above the substrate such as the height ofthe bridge downward to the substrate contact) and/or each contact 310may include a portion that extends downward (e.g., in the negativez-direction of FIG. 3) from leg 308 to the surface of the ROIC. Legs 308may be formed from one or more layers of conductive material such as,for example, titanium, nickel chromium, and/or other suitable conductivematerials.

In order to provide legs 308 having a width and a length that issufficient to provide suitable performance for microbolometer 300without reducing the fill-factor of an array of microbolometers in whichmicrobolometer 300 is included, legs 308 may be vertically oriented legsthat run along paths in and/or parallel to the x-y plane of FIG. 3 asshown and have an extended dimension that extends in a directionparallel to the z-direction of FIG. 3. Legs 308 may include bendportions 312. Bend portions 312 may have additional electrical couplingand/or support structures as described in further detail hereinafter.

A plane such as the x-y plane of FIG. 3 may be defined by the bridge ofthe microbolometer (e.g., the bridge may include a planar sensor layersuch as a resistive layer that defines a plane or a plane may be definedthat passes through multiple bridges in a microbolometer array) or bythe surface of a substrate (e.g., an ROIC substrate) to which themicrobolometer array is coupled and disposed above.

FIGS. 4A and 4B respectively show top and cross-sectional views of aconventional microbolometer 400 having horizontally oriented legs 406.As shown in the top view of FIG. 4A, a bridge 402 of microbolometer 400is connected by a bridge contact 404 to horizontally oriented leg 406having an extended dimension of width WP that extends in the x-y planeof FIG. 4A. In the cross sectional view of FIG. 4B, taken along line A-Aof FIG. 4A, it can more easily be seen that contact 404, leg 406, andresistive material 403 of microbolometer 400 all extend along the sameplane or parallel planes that are parallel to the x-y plane of FIG. 4B.

In contrast, FIGS. 5A and 5B respectively show top and cross-sectionalviews of a microbolometer 500 according to an embodiment of the presentdisclosure that includes a vertically oriented leg 308. As shown,vertically oriented leg 308 may have a width W in the x-y plane of FIGS.5A and 5B. Width W may be comparatively smaller than the width WP of aconventional microbolometer leg without sacrificing the overall volumeof the leg by allowing the leg 308 to extend in the vertical direction(e.g., in a direction parallel to the z-direction of FIGS. 5A and 5B) sothat vertical leg 308 is perpendicular to a plane defined by bridge 302(e.g., by resistive material 501 of bridge 302, by bridge contact 306,and or by an array of bolometer bridges formed at a common height abovean ROIC) and/or a plane defined by a surface of the substrate over whichthe bridge is formed.

As shown, according to an embodiment, a vertical leg 308 may include aconductive (e.g., metal) portion 506 and, if desired, insulatingmaterial 508 on one or more sides of the conductive portion. However,this is merely illustrative. According to various embodiments,conductive portion 506 may be partially or completely surrounded bydielectric material or may be free of dielectric material. Variousexamples of implementations of vertical legs 308 are describedhereinafter in connection with FIGS. 13A-13Q. However, first, processesthat may be used to form vertical bolometer legs such as vertical legs308 of FIGS. 3, 5A, and 5B will be discussed according to variousembodiments.

FIGS. 6A-6F show cross sectional side views of a portion of amicrobolometer array at various stages during production ofmicrobolometer legs for the microbolometer array.

Turning now to FIG. 6A, a portion 601 of a microbolometer array is shownhaving a contact 310 and a bridge 302. As shown, bridge 302 includes asensor layer (e.g., a layer of temperature sensitive resistive materialsuch as VOx) 606 and one or more additional layers 604 such as absorberlayers. As shown, contact 310 may be formed from a vertical conductiveportion such as metal stud 608 and one or more layers such as a metalcontact layer 614 in contact with metal stud 608. Contact 310 mayinclude additional layers such as a dielectric layer 616 disposed overthe metal layer 614 and an additional layer 612 such as a passivationlayer disposed under portions of metal layer 614. As shown, layer 612may be formed on a portion of a top surface 603 of a sacrificial layer600.

Sacrificial layer 600 may be formed from, for example, polyimide. Layers612 and 616 may be formed from, as examples, silicon dioxide or siliconnitride. Metal layer 614 may be formed from titanium, tungsten, copper,aluminum and/or other known metals.

Metal stud 608 may be conductively coupled to a conductive contact suchas contact 610 of a substrate such as a readout integrated circuit(ROIC) substrate such as a complementary metal-oxide-semiconductor(CMOS) ROIC. In the example of FIG. 6A, contact 610 is disposed in anoverglass layer 602 (e.g., a CMOS overglass layer) of the ROIC. Prior toforming vertical legs between the bridge 302 and the contact 310, bridge302 may be disposed on a sacrificial layer 600 that supports bridge 302and fills a gap between bridges of the microbolometer array and the ROICand runs continuously between the bridges and contacts of themicrobolometer array.

According to one embodiment, a process for forming vertical legs betweenbridge 302 and contact 310 may include depositing and patterning anadditional sacrificial layer 620 on sacrificial layer 600 as shown inFIG. 6B. Patterning the additional sacrificial layer 620 may includeforming openings 622 in the additional sacrificial layer (e.g., at leastpartially between the bridge 302 and the contact 310) so that remainingportions of additional sacrificial layer 620 have vertical sidewalls625. Openings 622 may extend into sacrificial layer 600 or may extendonly to the top surface 603 of sacrificial layer 600 (as examples).

Following the deposition and patterning of additional sacrificial layer620, a dielectric layer 624 may be deposited and patterned so thatportions of the dielectric layer 624 remain on sidewalls 625 ofadditional sacrificial layer 620 in openings 622 as shown in FIG. 6C. Ametal layer such as a leg metal layer 626 may then be deposited overcontact 310, portions of sacrificial layer 600, dielectric layer 624 onsidewalls 625, portions of additional sacrificial layer 620, and bridge302 as shown in FIG. 6D. If desired, openings may be formed in adielectric layer of contact 310 and bridge 302 to expose portions ofmetal layer 614 and sensor layer 606 so that metal layer 626 can bedeposited in contact with metal layer 614 and sensor layer 606. Metallayer 626 may be deposited in a blanket deposition process.

As shown in FIG. 6E, an additional dielectric layer 628 may be depositedover metal layer 626 and then metal layer 626 and additional dielectriclayer 628 may be etched (e.g., in a masked spacer etch process) toremove portions of metal layer 626 and additional dielectric layer 628from sacrificial layer 600 and additional sacrificial layer 620. In thisway, a dielectric-metal-dielectric stack may be formed vertically onsidewalls 625 of openings 622. Portions of thedielectric-metal-dielectric stack that are continuously coupled with theportions on sidewalls 625 may also remain on contact 310 and bridge 302,thereby forming bridge contact 306 and a leg metal contact with metallayer 614 of contact 310.

Dielectric layers 624 and 628 may be formed from, as examples, silicondioxide or a silicon nitride. Metal layer 626 may be a single metallayer formed form a homogeneous film of a single material or may includemultiple materials (e.g., multiple layers of the same or differentmaterials formed in multiple deposition operations). For example, metallayer 626 may be formed from titanium, tungsten, copper, aluminum and/orother known metals.

As shown in FIG. 6F, sacrificial layers 600 and 620 may then be removedto release bridge 302 and vertical legs 308 which remain suspended abovethe ROIC with a space 650 interposed between the vertical legs and theROIC. Although the vertical legs 308 of FIG. 6F appear to be floating,this is merely because of the particular cross section through thedevice that is shown. It will be understood by one skilled in the artthat vertical legs 308 of FIG. 6F run along the x-y plane of FIG. 6F as,for example, illustrated in FIG. 3 so that metal layer 626 forms acontinuous conductive path between bridge contact 306 and contact 310.Vertical legs 308 of FIG. 6F may include at least a portion that runsnon-perpendicularly to a plane defined by the surface 699 of substrate602. For example, vertical legs 308 may run along a path that isparallel to the surface 699. In another example, vertical legs 308 mayrun along a path that includes a portion that is parallel to surface 699and an additional portion that bends downward toward surface 699 at anon-perpendicular angle.

The process illustrated by FIGS. 6A-6F is merely illustrative. Accordingto various embodiments, vertical legs for a microbolometer array may beformed using other processes. For example, in one embodiment, a processsuch as the process shown in FIGS. 7A-7F may be performed to formvertical legs that are disposed below the plane at which bridge 302 isformed (e.g., in contrast with the vertical legs of FIG. 6F that aredisposed substantially in a common plane with bridge 302).

Turning now to FIG. 7A, a portion 701 of a microbolometer array is shownhaving a contact 310 and a bridge 302. As shown, bridge 302 includes asensor layer (e.g., a layer of temperature sensitive resistive materialsuch as VOx) 709 and one or more additional layers 707 such as absorberlayers. As shown, contact 310 may be formed from a vertical conductiveportion such as metal stud 708 and one or more layers such as a metalcontact layer 714 in contact with metal stud 708. Contact 310 mayinclude additional layers such as a dielectric layer 716 disposed overthe metal layer 714 and an additional layer 712 such as a passivationlayer disposed under portions of metal layer 714. As shown, passivationlayer 712 may be formed on a portion of a top surface 703 of asacrificial layer 700.

Sacrificial layer 700 may be formed from, for example, polyimide. Layers712 and 716 may be formed from, as examples, silicon dioxide or siliconnitride. Metal layer 714 may be formed from titanium, tungsten, copper,aluminum and/or other known metals.

Metal stud 708 may be conductively coupled to a conductive contact suchas contact 750 of a readout integrated circuit (ROIC) such as acomplementary metal-oxide-semiconductor (CMOS) ROIC. In the example ofFIG. 7A, contact 750 is disposed in an overglass layer 702 (e.g., a CMOSoverglass layer) of the ROIC. Prior to forming vertical legs between thebridge 302 and the contact 310, bridge 302 may be disposed on asacrificial layer 700 that supports bridge 302 and fills a gap betweenbridges of the microbolometer array and the ROIC and runs continuouslybetween the bridges and contacts of the microbolometer array.

According to one embodiment, a process for forming vertical legs betweenbridge 302 and contact 310 may include forming openings 704 in thesacrificial layer 700 that supports bridge 302 (e.g., by etching throughsurface 703) as shown in FIG. 7B. Openings 704 may be formed in aportion of sacrificial layer 700 that is disposed at least partiallybetween the bridge 302 and the contact 310 so that openings 704 havevertical sidewalls 705 at various locations between bridge 302 andcontact 310. As shown, sidewalls 705 may be located substantially belowa plane defined by bridge 302 (e.g., the x-y plane of FIG. 7B).

As shown in FIG. 7C, a dielectric layer 706 may be deposited andpatterned so that portions of the dielectric layer 706 remain onsidewalls 705 of sacrificial layer 700 in openings 704. Openings such asopenings 713 in layers 707 of bridge 302 and dielectric layer 716 mayalso be formed to expose portions of sensor layer 709 and metal layer714 respectively as shown in FIG. 7D.

A metal layer such as a leg metal layer 710 may then be deposited overcontact 310, portions of sacrificial layer 700, dielectric layer 706 onsidewalls 705, and bridge 302 as shown in FIG. 7E. Metal layer 710 maybe deposited in a blanket deposition process. As shown, portions ofmetal layer 710 may be formed within openings 713 (see FIG. 7D) and incontact with sensor layer 709 and metal layer 714.

An additional dielectric layer 711 (FIG. 7F) may be deposited over metallayer 710 and metal layer 710 and additional dielectric layer 711 may beetched (e.g., in a masked spacer etch process) to remove portions ofmetal layer 710 and additional dielectric layer 711 from sacrificiallayer 700. In this way, a dielectric-metal-dielectric stack may beformed vertically on sidewalls 705 of openings 704 and portions of thedielectric-metal-dielectric stack that are continuously coupled with theportions on sidewalls 705 may also remain on contact 310 and bridge 302,thereby forming bridge contact 306 and a leg metal contact with metallayer 714 of contact 310.

Dielectric layers 706 and 711 may be formed from, as examples, silicondioxide or a silicon nitride. Metal layer 710 may be a single metallayer formed form a homogeneous film of a single material or may includemultiple materials (e.g., multiple layers of the same or differentmaterials formed in multiple deposition operations). For example, metallayer 710 may be formed from titanium, tungsten, copper, aluminum and/orother known metals.

As shown in FIG. 7F, sacrificial layer 700 may then be removed torelease bridge 302 and vertical legs 308 formed from metal layer 710 anddielectric layers 706 and 711 that partially surround metal layer 710.As shown, vertical legs 308 remain suspended above the ROIC with a space720 interposed between the vertical legs and the ROIC. In this way,vertical legs 308 may be formed perpendicular to the x-y plane of FIG.7F and run along a path (e.g., as illustrated in FIG. 3) that isdisposed below the x-y plane of FIG. 7F between bridge 302 and contact310 so that metal layer 710 forms a continuous conductive path betweenbridge contact 306 and contact 310 via legs 308.

Vertical legs 308 of FIG. 7F may include at least a portion that runsnon-perpendicularly to a plane defined by the surface 799 of substrate702. For example, vertical legs 308 may run along a path that isparallel to the surface 799. In another example, vertical legs 308 mayrun along a path that includes a portion that is parallel to surface 799and an additional portion that bends downward toward surface 799 at anon-perpendicular angle.

In the example of FIG. 7F, the legs that couple bridge 302 to contact310 may include vertical portions 308 and horizontal portions 718 thatextend between bridge 302 and a first end of vertical leg 308 andbetween a second opposing end of vertical leg 308 and contact 310. Invarious embodiments, legs 308 may include any suitable combination ofvertical and horizontal portions for providing sufficient performancefor the microbolometer while avoiding reduction of the fill factor ofthe microbolometer array due to the area occupied by the legs.

FIGS. 8A-8C are cross sectional side views of a portion of amicrobolometer array at various stages during formation of vertical legsthat illustrate yet another alternative process of vertical legformation.

Turning now to FIG. 8A, a portion 801 of a microbolometer array is shownhaving a contact 310 and a bridge 302. As shown, bridge 302 includes asensor layer (e.g., a layer of temperature sensitive resistive materialsuch as VOx) 806 and one or more additional layers 807 such as absorberlayers. As shown, contact 310 may be formed from a vertical conductiveportion such as metal stud 803 and one or more layers such as a metalcontact layer 814 in contact with metal stud 803. Contact 310 mayinclude additional layers such as a dielectric layer 816 disposed overthe metal layer 814 and an additional layer 812 such as a passivationlayer disposed under portions of metal layer 814 and covering a topsurface of a sacrificial layer 800. Passivation layer 812 may extendbetween bridge 302 and contact 310 on the top surface sacrificial layer800.

Sacrificial layer 800 may be formed from, for example, polyimide. Layers812 and 816 may be formed from, as examples, silicon dioxide or siliconnitride. Metal layer 814 may be formed from titanium, tungsten, copper,aluminum and/or other known metals.

Metal stud 803 may be conductively coupled to a conductive contact suchas contact 809 of a readout integrated circuit (ROIC) such as acomplementary metal-oxide-semiconductor (CMOS) ROIC. In the example ofFIG. 8A, contact 809 is disposed in an overglass layer 802 (e.g., a CMOSoverglass layer) of the ROIC. Prior to forming vertical legs between thebridge 302 and the contact 310, bridge 302 may be disposed on asacrificial layer 800 that supports bridge 302 and fills a gap betweenbridges of the microbolometer array and the ROIC and runs continuouslybetween the bridges and contacts of the microbolometer array.

According to one embodiment, a process for forming vertical legs betweenbridge 302 and contact 310 may include forming openings 804 in thesacrificial layer 800 that supports bridge 302 and in the passivationlayer 812 that is disposed on the sacrificial layer as shown in FIG. 8A.Openings 804 may be formed in a portion of sacrificial layer 800 andpassivation layer 812 that is at least partially disposed between thebridge 302 and the contact 310 so that openings 804 have verticalsidewalls 805 at various locations between bridge 302 and contact 310.As shown, sidewalls 805 may be formed from a portion of sacrificiallayer 800 and passivation layer 812.

A metal layer such as a leg metal layer 808 may then be deposited (e.g.,over contact 310, on portions of the top surface of passivation layer812, on sidewalls 805 in contact with both sacrificial layer 800 andpassivation layer 812, on portions of sacrificial layer 800 in openings804, and on bridge 302) before a dielectric layer 810 is deposited(e.g., over metal layer 808) and then metal layer 808, dielectric layer810, and passivation layer 812 may be patterned (e.g., in a maskedspacer etch process) so that metal layer 808 remains on some of thesidewalls of openings 804, as shown in FIG. 8B. In this way, a metal legmay be formed vertically on some of the sidewalls of openings 804 andhorizontal portions 818 having metal layer 808 interposed betweenpassivation layer 812 and dielectric layer 810 may also remain onsacrificial layer 800.

Dielectric layer 810 may be formed from, as examples, silicon dioxide ora silicon nitride. Metal layer 808 may be a single metal layer formedform a homogeneous film of a single material or may include multiplematerials (e.g., multiple layers of the same or different materialsformed in multiple deposition operations). For example, metal layer 808may be formed from titanium, tungsten, copper, aluminum and/or otherknown metals.

As shown in FIG. 8C, sacrificial layer 800 may then be removed torelease bridge 302 and vertical legs 308 with horizontal portions 818.As shown, vertical legs 308 including horizontal portions 818 remainsuspended above the ROIC with a space 820 interposed between thevertical legs and the ROIC. Vertical legs having some horizontalportions such as those shown in FIG. 8C may be less prone to movementand/or damage than legs having only vertical portions. Vertical legs 308including horizontal portions 818 may form a continuous conductive pathbetween bridge contact 306 and contact 310 via legs 308.

Vertical legs 308 of FIG. 8C may include at least a portion that runsnon-perpendicularly to a plane defined by the surface 899 of substrate802. For example, vertical legs 308 may run along a path that isparallel to the surface 899. In another example, vertical legs 308 mayrun along a path that includes a portion that is parallel to surface 899and an additional portion that bends downward toward surface 899 at anon-perpendicular angle.

It will be appreciated that the processes described above in connectionwith FIGS. 6A-8C can be modified, rearranged, and/or omitted to formvertical bolometer legs having various shapes, sizes, orientations, andarrangements as desired for various purposes. FIGS. 9, 10, 11, 12,13A-13Q, 14, and 15 show various arrangements of vertical legs andassociated contacts or bridges that can be formed for microbolometerarrays. In particular, FIGS. 9 and 10 show portions of a microbolometerarray (prior to release by removal of a sacrificial layer) havingvertical legs formed below the plane of the bridge in the vicinity of acontact and a bridge, respectively, of a microbolometer, according toone embodiment. FIGS. 11 and 12 show portions of a microbolometer arrayhaving vertical legs formed below the plane of the bridge in thevicinity of a contact and a bridge, respectively, of a microbolometer,according to another embodiment. FIGS. 13A-13Q show various arrangementsof metal and insulation for vertical legs for a microbolometer. FIGS. 14and 15 show portions of a microbolometer array having vertical legsformed at or above the plane of the bridge in the vicinity of a contactand a bridge, respectively, of a microbolometer, according to anotherembodiment.

As shown in FIG. 9, at a particular stage of production, a portion ofmetal layer 714 may be formed on sacrificial layer 700 and a portion ofdielectric layer 706 may extend over the portion of metal layer 714 thatis formed on the sacrificial layer, over a vertical portion of metallayer 714 that is formed on stud 708, and over a horizontal portion ofmetal layer 714 that is formed on top of stud 708 such that the portionof dielectric layer 706 that is disposed above the top surface ofsacrificial layer 700 is symmetric on multiple sides of stud 708.Sacrificial layer 700 may then be removed.

A process that results in the structure of FIG. 9 for contact 310 mayalso form a bridge as shown in FIG. 10 according to an embodiment. Asshown in FIG. 10, bridge 302 may include bridge dielectric layers 1000and 1002 disposed on opposing sides of sensor layer 606. Dielectriclayer 706 may extend vertically from a vertical leg structure 308 andover a portion of bridge dielectric 1002. Metal layer 710 may cover theportion of dielectric layer 706 that extends vertically from thevertical leg structure 308 and over the portion of bridge dielectric1002 and the metal layer may extend through bridge dielectric 1002 andleg dielectric 706 to contact sensor layer 606.

In an alternative embodiment, as shown in FIG. 11, metal layer 710 maybe asymmetric about the top of stud 708 so that metal layer 710 remainsin contact with metal layer 714 of contact 310 on the side of stud 708on which the vertical legs 308 are formed, thereby increasing thecontact area between layers 710 and 714. Following formation of thestructures of FIG. 11 as shown, sacrificial layer 700 may be removed.

A process that results in the structure of FIG. 11 for contact 310 mayalso form a bridge as shown in FIG. 12 according to an embodiment. Asshown in FIG. 12, a portion of metal layer 710 may be formed directly ona portion of bridge dielectric 1002 so that metal layer 710 passes overthe portion of bridge dielectric 1002 and through bridge dielectric 1002to contact sensor layer 606.

FIGS. 13A-13Q each show a cross sectional view of an exemplaryimplementation of a vertical bolometer leg such as vertical legs 308 asdescribed herein. As shown in FIG. 13A, a vertical bolometer leg mayinclude a substantially vertical conductive (e.g., metal) layer 1300that is disposed between first and second substantially verticaldielectric layers 1302 and 1304 that have a common height H with thevertical conductive layer 1300. In the configuration of FIG. 13A, thevertical leg may have a width that is substantially the same along theheight of the vertical leg and substantially equal to the sum of thewidths of the layers 1300, 1302, and 1304.

In general, a vertical bolometer leg may have a first dimension (e.g., aheight H) that extends in a direction that is perpendicular to a planedefined by the associated bolometer bridge and/or a substrate, a seconddimension (e.g., a width W) that extends in a direction that is parallelto the plane of the bridge and/or the substrate, and a third dimensionthat extends along and defines a signal path, where the path may includea portion that extends in a direction parallel to the plane of thebridge and/or the substrate, and where the second dimension issubstantially smaller than the first dimension.

As shown in FIG. 13B, in one embodiment, dielectric layer 1302 mayextend above the top of conductive layer 1300 and run horizontally overthe top of conductive layer 1300 and dielectric layer 1304. As shown inFIG. 13C, in one embodiment, conductive layer 1300 may have a heightthat is shorter than the height of dielectric layer 1302 and dielectriclayer 1302 may run underneath the bottom of conductive layer 1300 anddielectric layer 1304.

As shown in FIG. 13D, in one embodiment, dielectric layer 1302 mayextend above the top of conductive layer 1300 and run horizontally overthe top of conductive layer 1300 and dielectric layer 1304 andconductive layer 1300 may have a height that is shorter than the heightof dielectric layer 1302 and dielectric layer 1304 may run underneaththe bottom of conductive layer 1300 to dielectric layer 1302. As shownin FIG. 13E, in one embodiment, conductive layer 1300 may have a heightthat is shorter than the height of dielectric layer 1302, dielectriclayer 1304 may run underneath the bottom of conductive layer 1300 todielectric layer 1302, and a horizontal dielectric layer 1306 may coverthe top of layers 1300, 1302, and 1304.

As shown in FIG. 13F, in one embodiment, conductive layer 1300 anddielectric layers 1302 and 1304 may have a common height and ahorizontal dielectric layer 1306 may cover the top of layers 1300, 1302,and 1304. As shown in FIG. 13G, in one embodiment, conductive layer 1300may have a vertical portion and a horizontal portion such thatconductive layer has, in cross section, an “L” shape. In theconfiguration of FIG. 13G, dielectric layer 1304 runs vertically alongthe vertical portion of conductive layer 1300 and horizontally under thevertical and horizontal portions of conductive layer 1300 and dielectriclayer 1302 runs vertically along the vertical portion of conductivelayer 1300, horizontally over the top of the horizontal portion ofconductive layer 1300, and vertically past the horizontal portion ofconductive layer 1300 to the bottom of the vertical leg.

As shown in FIG. 1311, in one embodiment, conductive layer 1300 may befree of any surrounding dielectric material. As shown in FIG. 131, inone embodiment, conductive layer 1300 may have one side covered bydielectric layer 1304 and an opposing side that is free of dielectricmaterial. As shown in FIG. 13J, in one embodiment, a conductive layer1300 that has one side covered by dielectric layer 1302 and an opposingside that is free of dielectric material may have a height that isshorter than the height of the vertical leg and dielectric layer 1302may run underneath the bottom of conductive layer 1300. As shown in FIG.13K, in one embodiment, a conductive layer 1300 that has one sidecovered by dielectric layer 1302 and an opposing side that is free ofdielectric material may have a vertical portion and a horizontal portionthat runs over the top of dielectric layer 1302.

As shown in FIG. 13L, in one embodiment, a conductive layer 1300 thathas one side covered by dielectric layer 1304 and an opposing side thatis free of dielectric material may have a first vertical portion, ahorizontal portion that runs over the top of dielectric layer 1304, anda second vertical portion that is offset from the first verticalportion. In the configuration of FIG. 13L, dielectric layer 1304 mayhave a vertical portion that runs along the first vertical portion ofconductive layer 1300 and a horizontal portion that runs under the firstvertical portion of conductive layer 1300 to the second vertical portionof conductive layer 1300.

As shown in FIG. 13M, conductive layer 1300 may include a verticalportion and a horizontal portion 1308 that extends horizontally from thebottom of the vertical portion of conductive layer 1300 so thatconductive layer 1300 and horizontal portion 1308 form an “L” shape. Inthe example of FIG. 13M, conductive layer 1300 is covered on a firstside by dielectric (insulating) layer 1302, on another side bydielectric (insulating) layer 1304, and along a bottom surface ofhorizontal portion 1308 by insulating (dielectric layer 1312).

As shown in FIG. 13N, in one embodiment, horizontal portion 1308 and thepart of the vertical portion that is below the top surface of thevertical portion may be substantially surrounded by one or moredielectric layers such as dielectric layers 1302, 1304, and 1312 so thatthe top end of the vertical portion of conductive layer 1300 is free ofdielectric material.

As shown in FIG. 13O, in one embodiment, conductive portion 1300 mayhave a vertical portion, a first horizontal portion that extends in afirst direction from the top of the vertical portion, a secondhorizontal portion that extends in an opposing second direction from thebottom of the vertical portion, and an additional portion that fills thespace beneath a horizontal dielectric layer 1304 formed under the firsthorizontal portion. In the configuration of FIG. 13O, the firsthorizontal portion, the vertical portion and top of the secondhorizontal portion of conductive layer 1300 are covered on one side bydielectric layer 1302.

As shown in FIG. 13P, in one embodiment, conductive layer 1300 may havea vertical portion, a first horizontal portion that extends in a firstdirection from the top of the vertical portion, and a second horizontalportion that extends in an opposing second direction from the bottom ofthe vertical portion. In the configuration of FIG. 13P, the firsthorizontal portion, the vertical portion and top of the secondhorizontal portion of conductive layer 1300 are covered on one side bydielectric layer 1302 and dielectric layer 1304 runs under and fills thespace under the first horizontal portion of conductive layer 1300. Asshown in FIG. 13Q, a conductive layer having a vertical portion, a firsthorizontal portion that extends in a first direction from the top of thevertical portion, and a second horizontal portion that extends in anopposing second direction from the bottom of the vertical portion may besubstantially surrounded by an insulating material 1312.

As shown in FIG. 14, at a particular stage of production for verticalbolometer legs formed above and perpendicular to surface 603 of asacrificial layer such as sacrificial layer 600 (e.g., the sacrificiallayer upon which the bridge structures for one or more microbolometersare formed), a portion of metal layer 614 may be formed on sacrificiallayer 600 and a portion of dielectric layer 624 may extend over theportion of metal layer 614 that is formed on the sacrificial layer, overa vertical portion of metal layer 614 that is formed on stud 608, andover a horizontal portion of metal layer 614 that is formed on top ofstud 608. Dielectric layer 624, leg metal layer 626, and dielectriclayer 628 may form a horizontal portion 1400 that extends horizontallyfrom contact 310 and turns perpendicularly to form vertical leg portion308. Sacrificial layer 600 may then be removed.

A process that results in the structure of FIG. 14 for contact 310 mayalso form a bridge as shown in FIG. 15 according to an embodiment. Asshown in FIG. 15, bridge 302 may include bridge dielectric layers 1500and 1502 disposed on opposing sides of sensor layer 606. Dielectriclayer 624, metal layer 626, and dielectric layer 628 may form a stackthat includes vertical leg portions 308 and a portion 1504 that extendshorizontally from a vertical leg portion 308 to bridge 302. As shown,metal layer 626 may cover a portion of dielectric layer 624 that extendshorizontally from the vertical leg structure 308 and over a portion ofbridge dielectric 1502 and may pass through bridge dielectric 1502 andleg dielectric 624 to contact sensor layer 606.

FIG. 16 shows a top view of a portion of a vertical leg 308 in a bendregion 312. FIGS. 17 and 18 show cross sectional side views of exemplaryimplementations of the bend region 312 taken along the line x-x of FIG.16. As shown in FIG. 17, according to one embodiment, bend region 312may include a pad 1700 formed at the bottom of a vertical conductivelayer 1702 that is interposed between vertical dielectric layers 1704and 1706 of the vertical leg. Pad 1700 may be formed from metal,dielectric materials, or a combination of metal and dielectric materials(as examples). As shown in FIG. 18, according to one embodiment, bendregion 312 may include a metal pad 1800 formed over the top of verticalconductive layer 1702 and vertical dielectric layers 1704 and 1706 ofthe vertical leg. Pad 1800 may be formed from metal, dielectricmaterials, or a combination of metal and dielectric materials (asexamples).

FIG. 19 is a cross sectional side view of a portion of a microbolometerarray at a particular stage of production showing how, in oneembodiment, at least a portion of a vertical leg structure may be formedbeneath the bridge 302 of a microbolometer. As shown in FIG. 19, bridge302 may include a sensor layer 606 disposed between bridge dielectriclayers 1908 and 1910. Bridge dielectric layer 1910 may be formed on afirst sacrificial layer 1904 that is interposed between bridgedielectric layer 1910 and a vertical leg structure 1906 that runsbeneath the bridge dielectric layer 1910 and overglass 1902 of an ROICfor the microbolometer array. At the stage of production shown in FIG.19, a second sacrificial layer 1900 may be disposed between the verticalleg structure 1906 and overglass 1902.

In the configuration shown in FIG. 19, sensor layer 606 of bridge 302includes a vertical portion that runs downward from the bridge 302 andturns horizontally to form a portion of bridge contact 306. As shown, aconductive layer such as conductive layer 1911 may couple sensormaterial 606 in bridge contact region 306 to the vertical leg structure1906. Vertical leg structure 1906 may extend to a contact such as a studcontact or basket contact that couples the vertical leg structure 1906to a contact on the ROIC (e.g., a contact formed partially or completelywithin overglass layer 1902). Vertical leg structure 1906 may couple toa dedicated contact structure for the bridge 302 underneath which it isformed and/or may be coupled to a shared contact with an adjacentmicrobolometer.

FIG. 20 is a flowchart of illustrative operations that may be performedfor forming vertical microbolometer legs for coupling a microbolometerbridge to a ROIC contact structure according to an embodiment.

At block 2000, an imaging device having contact structures and bolometerbridge structures such as microbolometer bridge structures may beprovided. The imaging device may include a partially fabricated focalplane array on which a sacrificial layer such as a polyimide layer isformed on a substrate such as a readout integrated circuit and thebridge structures are formed on the sacrificial layer. In someembodiments, an etch stop layer may be formed on the sacrificial layer.However, in other embodiments, the sacrificial layer may be free of anyetch stop material. The contact structures may include an electricalcontact on the readout integrated circuit and, if desired conductiveelements that extend from the electrical contact on the ROIC throughsome or all of the sacrificial layer. The conductive elements mayinclude a stud or a basket contact and, if desired, one or moreadditional structures such as passivation layers, metal layers, and/ordielectric layers formed over the conductive elements.

At block 2002, an additional sacrificial layer may be deposited andpatterned over or on the sacrificial layer. In embodiments, in which anetch stop layer is provided on the sacrificial layer, the additionalsacrificial layer may be deposited on the etch stop layer so thatportions of the etch stop layer are formed between the sacrificial layerand the additional sacrificial layer. Patterning the additionalsacrificial layer may include etching the additional sacrificial layerto form openings in the additional sacrificial layer at least partiallybetween the bridge structures and the contact structures.

At block 2004, a first leg dielectric material may be formed at least onsidewalls of the openings in the patterned additional sacrificial layer.Forming the first leg dielectric material on the sidewalls of theopenings may include depositing the first leg dielectric layer andperforming a spacer etch of the first leg dielectric layer. The etch mayalso leave portions of the first leg dielectric layer on portions of thecontact structures and/or the bridge structures as desired.

At block 2006, one or more conductive layers such as a leg metal layermay be deposited (e.g., using a blanket metal deposition) and patternedon the first leg dielectric material on the sidewalls of the openingsand over at least some of the contact structures and the bridgestructures. The leg metal layer may be formed in contact with a metallayer of the contact structures and with a sensor layer of the bridgestructures.

At block 2008, a second leg dielectric layer may be deposited andpatterned on the metal layer. Patterning the second leg dielectric layermay include depositing the second leg dielectric layer over the legmetal layer prior to patterning the leg metal layer and performing anin-situ dielectric and metal etch of the leg metal layer and the secondleg dielectric layer.

At block 2010, the sacrificial layer and the additional sacrificiallayer may be removed to release the bridge structures and the verticalleg structures formed from the first and second leg dielectric layersand the leg metal layers so that the bridge and legs are suspended abovethe readout integrated circuit and the contact structures are coupled tothe bridge structures by the vertical leg structures. In embodiments, inwhich an etch stop layer is provided on the sacrificial layer, portionsof the etch stop layer may also be removed.

FIG. 21 is a flowchart of illustrative operations that may be performedfor forming vertical microbolometer legs for coupling a microbolometerbridge to a ROIC contact structure according to another embodiment.

At block 2100, an imaging device having contact structures and bolometerbridge structures such as microbolometer bridge structures may beprovided. The imaging device may include a partially fabricated focalplane array on which a sacrificial layer such as a polyimide layer isformed on a readout integrated circuit and the bridge structures areformed on the sacrificial layer. The contact structures may include anelectrical contact on the readout integrated circuit and, if desiredconductive elements that extend from the electrical contact on the ROICthrough some or all of the sacrificial layer. The conductive elementsmay include a stud or a basket contact and, if desired, one or moreadditional structures such as passivation layers, metal layers, and/ordielectric layers formed over the conductive elements.

At block 2102, the sacrificial layer may be etched to form openings inthe sacrificial layer at least partially between the bridge structuresand the contact structures.

At block 2104, a first leg dielectric material may be formed at least onsidewalls of the openings in the sacrificial layer. Forming the firstleg dielectric material on the sidewalls of the openings may includedepositing the first leg dielectric layer and performing a spacer etchof the first leg dielectric layer. The etch may also be performed toleave portions of the first leg dielectric layer on portions of thecontact structures and/or the bridge structures as desired.

At block 2106, openings may be formed in a dielectric layer of thecontact structures and the bridge structures. Forming the openings inthe dielectric layer of the contact structures and the bridge structuresmay expose portions of a metal layer of the contact structures and/or asensor layer of the bridge structures.

At block 2108, one or more conductive layers such as a leg metal layermay be deposited (e.g., using a blanket metal deposition) and patternedon the first leg dielectric material on the sidewalls of the openingsand over at least some of the contact structures and the bridgestructures. The leg metal layer may be formed in contact with theexposed portions of the metal layer of the contact structures and thesensor layer of the bridge structures.

At block 2110, a second leg dielectric layer may be deposited andpatterned on the metal layer. Patterning the second leg dielectric layermay include depositing the second leg dielectric layer over the legmetal layer prior to patterning the leg metal layer and performing anin-situ dielectric and metal etch of the leg metal layer and the secondleg dielectric layer.

At block 2112, the sacrificial layer may be removed to release thebridge structures and the vertical leg structures formed from the firstand second leg dielectric layers and the leg metal layers so that thebridge and legs are suspended above the readout integrated circuit andthe contact structures are coupled to the bridge structures by thevertical leg structures.

FIG. 22 is a flowchart of illustrative operations that may be performedfor forming vertical microbolometer legs for coupling a microbolometerbridge to a ROIC contact structure according to another embodiment.

At block 2200, an imaging device having contact structures and bolometerbridge structures such as microbolometer bridge structures may beprovided. The imaging device may include a partially fabricated focalplane array on which a sacrificial layer such as a polyimide layer isformed on a readout integrated circuit, a passivation layer is formed onat least a portion of the sacrificial layer and the bridge structuresare formed on the sacrificial layer. The contact structures may includean electrical contact on the readout integrated circuit and, if desiredconductive elements that extend from the electrical contact on the ROICthrough some or all of the sacrificial layer. The conductive elementsmay include a stud or a basket contact and, if desired, one or moreadditional structures such a portion of the passivation layer, metallayers, and/or dielectric layers formed over the conductive elements.

At block 2202, the sacrificial layer and the passivation layer may beetched to form openings in the sacrificial layer and the passivationlayer at least partially between the bridge structures and the contactstructures.

At block 2204, one or more conductive layers such as a leg metal layermay be deposited (e.g., using a blanket metal deposition) and patternedon the sidewalls of the openings and over at least some of the contactstructures, the bridge structures, and portions of the passivation layeron the sacrificial layer.

At block 2206, a leg dielectric layer may be deposited and patterned onthe metal layer. Patterning the leg dielectric layer may includedepositing the leg dielectric layer over the leg metal layer prior topatterning the leg metal layer and performing an in-situ dielectric andmetal etch of the leg metal layer and the second leg dielectric layer.

At block 2208, the sacrificial layer may be removed to release thebridge structures and the vertical leg structures formed from portionsof the passivation layer, the leg dielectric layer and the leg metallayer so that the bridge and legs are suspended above the readoutintegrated circuit and the contact structures are coupled to the bridgestructures by the vertical leg structures.

The process described above for forming vertical microbolometer legs aremerely illustrative. According to various embodiments, vertical legs fora microbolometer array may be formed using other processes. For example,in one embodiment, a process such as the process shown in FIGS. 23A-23Fmay be performed to form vertical legs using an etch stop layer.

FIGS. 23A-23F show cross sectional side views of a portion of amicrobolometer array at various stages during production ofmicrobolometer legs for the microbolometer array.

Turning now to FIG. 23A, a portion 2398 of a microbolometer array isshown having a contact 310 and a bridge 302. As shown, bridge 302includes a sensor layer (e.g., a layer of temperature sensitiveresistive material such as VOx) 2306 and one or more additional layers2304 such as absorber layers. As shown, contact 310 may be formed from avertical conductive portion such as metal stud 2308 and one or morelayers such as a metal contact layer 2314 in contact with metal stud2308. Contact 310 may include additional layers such as a passivationlayer 2316 disposed under portions of metal layer 2314. As shown, anadditional layer such as an etch stop layer 2303 (e.g., a layer ofdielectric material) may be formed on sacrificial layer 2300 and mayextend to form a portion of bridge 302 and/or contact 310.

Sacrificial layer 2300 may be formed from, for example, polyimide.Layers 2303 and 2316 may be formed from, as examples, silicon dioxide orsilicon nitride. Metal layer 2314 may be formed from titanium, tungsten,copper, aluminum and/or other known metals.

Metal stud 2308 may be conductively coupled to a conductive contact suchas contact 2310 of a substrate such as a readout integrated circuit(ROIC) substrate such as a complementary metal-oxide-semiconductor(CMOS) ROIC. In the example of FIG. 23A, contact 2310 is disposed in anoverglass layer 2302 (e.g., a CMOS overglass layer) of the ROIC. Priorto forming vertical legs between the bridge 302 and the contact 310,bridge 302 may be disposed on sacrificial layer 2300 so that sacrificiallayer 2300 fills a gap between bridges of the microbolometer array andthe ROIC and runs continuously between the bridges and contacts of themicrobolometer array.

According to one embodiment, a process for forming vertical legs betweenbridge 302 and contact 310 may include depositing and patterning anadditional sacrificial layer 2320 on etch stop layer 2303 as shown inFIG. 23B. Patterning the additional sacrificial layer 2320 may includeforming openings 2322 in the additional sacrificial layer (e.g., atleast partially between the bridge 302 and the contact 310) so thatremaining portions of additional sacrificial layer 2320 have verticalsidewalls 2325. Openings 2322 may extend to the top surface 2301 of etchstop layer 2303.

Following the deposition and patterning of additional sacrificial layer2320, a dielectric layer 2324 may be deposited and patterned so thatportions of the dielectric layer 2324 remain on sidewalls 2325 ofadditional sacrificial layer 2320 in openings 2322 as shown in FIG. 23C.A metal layer such as a leg metal layer 2326 may then be deposited overcontact 310, portions of etch stop layer 2303, dielectric layer 2324 onsidewalls 2325, portions of additional sacrificial layer 2320, andbridge 302 as shown in FIG. 23D. If desired, openings may be formed inportions of etch stop layer 2303 that are disposed over contact 310 andbridge 302 to expose portions of metal layer 2314 and sensor layer 2306so that metal layer 2326 can be deposited in contact with metal layer2314 and sensor layer 2306. Metal layer 2326 may be deposited in ablanket deposition process.

As shown in FIG. 23E, an additional dielectric layer 2328 may bedeposited over metal layer 2326 and then metal layer 2326 and additionaldielectric layer 2328 may be etched (e.g., in a masked spacer etchprocess) to remove portions of metal layer 2326 and additionaldielectric layer 2328 from etch stop layer 2303 and additionalsacrificial layer 2320. In this way, a dielectric-metal-dielectric stackmay be formed vertically on sidewalls 2325 of openings 2322. Portions ofthe dielectric-metal-dielectric stack that are continuously coupled withthe portions on sidewalls 2325 may also remain on contact 310 and bridge302, thereby forming bridge contact 306 and a leg metal contact withmetal layer 2314 of contact 310.

Dielectric layers 2324 and 2328 may be formed from, as examples, silicondioxide or a silicon nitride. Metal layer 2326 may be a single metallayer formed form a homogeneous film of a single material or may includemultiple materials (e.g., multiple layers of the same or differentmaterials formed in multiple deposition operations). For example, metallayer 2326 may be formed from titanium, tungsten, copper, aluminumand/or other known metals.

As shown in FIG. 23F, sacrificial layers 2300 and 2320 and portions ofetch stop layer 2303 may then be removed to release bridge 302 andvertical legs 308 which remain suspended above the ROIC with a space2350 interposed between the vertical legs and the ROIC. Vertical legs308 of FIG. 23F may include at least a portion that runsnon-perpendicularly to a plane defined by the surface 2399 of substrate2302. For example, vertical legs 308 may run along a path that isparallel to the surface 2399. In another example, vertical legs 308 mayrun along a path that includes a portion that is parallel to surface2399 and an additional portion that bends downward toward surface 2399at a non-perpendicular angle.

FIG. 24 shows a cross-sectional side view of a microbolometer bridgethat is coupled to legs formed beneath the bridge, according to anembodiment. In the example of FIG. 24, bridge 302 includes a sensorlayer 2400 formed substantially between bridge dielectric layers 2402and 2404. Sensor layer 240 (e.g., a temperature sensitive resistivematerial, such as VOx) may include one or more horizontal portions thatextend in a plane that is parallel to the surface of a substrate overwhich bridge 302 is formed and may include portions 2406 that extenddownward from the horizontal portions in the direction of the substrate(e.g., perpendicularly to the surface of the substrate. Portions 2406may extend to contact one or more legs such as legs 2420 formed beneaththe bridge 302 (e.g., disposed at least partially between bridge 302 andthe substrate over which the bridge is disposed).

As shown in FIG. 24, legs 2420 are formed form a conductive materialhaving a horizontal portion 2408 in contact with sensor layer 2306 and avertical portion 2410 that extends perpendicularly to horizontal portion2408. However, this is merely illustrative. In various embodiments, legs2420 may include vertical and/or horizontal portions and/or may becovered partially or completely in an insulating material as in, forexample, any of the examples described herein.

Illustrative operations that may be performed to form a bridge of thetype shown in FIG. 24 are shown in FIG. 25.

At block 2500, an imaging device having contact structures that areformed on and/or in a sacrificial layer may be provided. The imagingdevice may include a partially fabricated focal plane array on which asacrificial layer such as a polyimide layer is formed on a substratesuch as a readout integrated circuit substrate. The contact structuresmay include an electrical contact on the substrate and, if desiredconductive elements that extend from the electrical contact on the ROICthrough some or all of the sacrificial layer. The conductive elementsmay include a stud or a basket contact and, if desired, one or moreadditional structures such as passivation layers, metal layers, and/ordielectric layers formed over the conductive elements.

At block 2502, openings may be formed in the sacrificial layer.

At block 2504, a first leg dielectric material may be formed at least onsidewalls of the openings in the sacrificial layer. Forming the firstleg dielectric material on the sidewalls of the openings may includedepositing the first leg dielectric layer and performing a spacer etchof the first leg dielectric layer.

At block 2506, one or more conductive layers such as a leg metal layermay be deposited (e.g., using a blanket metal deposition) and patternedon the first leg dielectric material that is on the sidewalls of theopenings and over at least some of the contact structures. The leg metallayer may be formed in contact with a metal layer of the contactstructures.

At block 2508, a second leg dielectric layer may be deposited andpatterned on the leg metal layer. Patterning the second leg dielectriclayer may include depositing the second leg dielectric layer over theleg metal layer prior to patterning the leg metal layer and performingan in-situ dielectric and metal etch of the leg metal layer and thesecond leg dielectric layer.

At block 2510, an additional sacrificial layer may be deposited on thesacrificial layer.

At block 2512, one or more bolometer bridge contacts may be formed inthe second sacrificial layer.

At block 2514, a first bridge dielectric layer may be deposited.

At block 2516, one or more contacts may be formed in the first bridgedielectric layer and the underlying second leg dielectric layer on theleg metal layer for connection to the leg metal layer.

At block 2518, a bolometer resistive sensing material (e.g., atemperature sensitive resistive material such as VOx) may be depositedand patterned to form sensor layers of the bolometer bridges.

At block 2520, as second bridge dielectric material may be deposited andpatterned, thereby defining a bridge area of each microbolometer formedover at least portions of the underlying leg materials.

At block 2522, the sacrificial layer and the additional sacrificiallayer may be removed to release the bridge structures and the verticalleg structures so that the bridge and legs that are formed beneath thebridge are suspended above the substrate and the contact structures arecoupled to the bridge structures by the vertical leg structures.

Where applicable, various embodiments of the invention may beimplemented using hardware, software, or various combinations ofhardware and software. Where applicable, various hardware componentsand/or software components set forth herein may be combined intocomposite components comprising software, hardware, and/or both withoutdeparting from the scope and functionality of the invention. Whereapplicable, various hardware components and/or software components setforth herein may be separated into subcomponents having software,hardware, and/or both without departing from the scope and functionalityof the invention. Where applicable, it is contemplated that softwarecomponents may be implemented as hardware components and vice-versa.

Software, in accordance with the invention, such as program code and/ordata, may be stored on one or more computer readable mediums. It is alsocontemplated that software identified herein may be implemented usingone or more general purpose or specific purpose computers and/orcomputer systems, networked and/or otherwise. Where applicable, orderingof various steps described herein may be changed, combined intocomposite steps, and/or separated into sub-steps to provide featuresdescribed herein.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

What is claimed as new and desired to be protected is:
 1. A method of forming an infrared imaging device, the method comprising: providing a device having a bolometer bridge structure and a contact structure, wherein the bolometer bridge structure is formed on a sacrificial layer, and wherein the contact structure extends through the sacrificial layer; depositing an additional sacrificial layer over the sacrificial layer; forming openings in the additional sacrificial layer; forming a leg structure having at least a first portion that runs between the bolometer bridge structure and the contact structure, wherein the forming of the leg structure comprises forming portions of a first layer on sidewalls of the openings, and wherein the leg structure comprises the portions of the first layer; and removing the sacrificial layer and the additional sacrificial layer to suspend the bolometer bridge structure and the leg structure above a substrate of the infrared imaging device, wherein the first portion of the leg structure has a first dimension that extends in a first direction that is substantially perpendicular to a plane defined by a surface of the substrate, wherein the first portion of the leg structure has a second dimension that extends in a second direction that is substantially parallel to the plane, wherein the portions of the first layer have a first dimension that extends in the first direction and a second dimension that extends in the second direction, and wherein the first dimension of the portions of the first layer is greater than the second dimension of the portions of the first layer.
 2. The method of claim 1, wherein the forming of the leg structure further comprises forming first portions of a second layer on the portions of the first layer, wherein the leg structure further comprises the first portions of the second layer.
 3. The method of claim 1, wherein: the infrared imaging device comprises a focal plane array; and the method further comprises integrating the focal plane array into an infrared camera.
 4. The method of claim 1, wherein the device includes an etch stop layer on the sacrificial layer and wherein the depositing of the additional sacrificial layer over the sacrificial layer comprises depositing the additional sacrificial layer on the etch stop layer.
 5. The method of claim 1, wherein the first layer is a metal layer or a dielectric layer.
 6. The method of claim 2, wherein the forming of the leg structure further comprises: depositing the first layer on portions of the sacrificial layer and the additional sacrificial layer; performing a spacer etch of the first layer so that the portions of the first layer remain on the sidewalls; depositing the second layer over the portions of the first layer on the sidewalls, over the bolometer bridge structure, and over the contact structure of the device; depositing a third layer over the second layer; and removing second portions of the second layer and portions of the third layer, wherein the second portions of the second layer are removed such that the first portions are on a side of the portions of the first layer.
 7. The method of claim 2, wherein the first portions of the second layer have a first dimension that extends in the first direction and a second dimension that extends in the second direction, and wherein the first dimension of the first portions of the second layer is greater than the second dimension of the first portions of the second layer.
 8. The method of claim 2, wherein the first layer is a dielectric layer, wherein the second layer is a metal layer, and wherein the leg structure runs non-perpendicularly to the plane.
 9. The method of claim 2, wherein the forming of the leg structure further comprises: depositing the second layer over the portions of the first layer, over the bolometer bridge structure, and over the contact structure; and removing second portions of the second layer such that the first portions remain on a side of the portions of the first layer.
 10. The method of claim 2, wherein the portions of the first layer and the first portions of the second layer are adjacent to each other and stacked in a direction along the plane.
 11. The method of claim 2, wherein the forming of the leg structure further comprises: forming portions of a third layer on the first portions of the second layer, wherein the leg structure further comprises the portions of the third layer, wherein the portions of the first layer are on a first side of the first portions of the second layer, wherein the portions of the third layer are on a second side of the first portions of the second layer, and wherein the first side is opposite the second side.
 12. The method of claim 11, wherein: the first layer is a dielectric layer, the second layer is a metal layer, the third layer is a dielectric layer, and the portions of the first layer, the first portions of the second layer, and the portions of the third layer are adjacent to each other and stacked in a direction along the plane.
 13. A method of forming an infrared imaging device, the method comprising: providing a device having a bolometer bridge structure and a contact structure, wherein the bolometer bridge structure is formed on a sacrificial layer, and wherein the contact structure extends through the sacrificial layer; forming openings in the sacrificial layer; forming a leg structure having at least a first portion that runs between the bolometer bridge structure and the contact structure, wherein the forming of the leg structure comprises forming portions of a first layer on sidewalls of the openings, and wherein the leg structure comprises the portions of the first layer; and removing the sacrificial layer to suspend the bolometer bridge structure and the leg structure above a substrate of the infrared imaging device, wherein the first portion of the leg structure has a first dimension that extends in a first direction that is substantially perpendicular to a plane defined by a surface of the substrate, wherein the first portion of the leg structure has a second dimension that extends in a second direction that is substantially parallel to the plane, wherein the portions of the first layer have a first dimension that extends in the first direction and a second dimension that extends in the second direction, and wherein the first dimension of the portions of the first layer is greater than the second dimension of the first layer.
 14. The method of claim 13, wherein: the infrared imaging device comprises a focal plane array; and the method further comprises integrating the focal plane array into an infrared camera.
 15. The method of claim 13, wherein: the device includes a passivation layer formed on the sacrificial layer, wherein the forming of the openings comprises forming the openings in the sacrificial layer and the passivation layer; the first layer is a metal layer formed over portions of the passivation layer, over the bolometer bridge structure, and over the contact structure; and the forming of the leg structure further comprises: forming a dielectric layer over the metal layer; and removing portions of the metal layer and the dielectric layer.
 16. The method of claim 15, wherein: the infrared imaging device comprises a focal plane array; and the method further comprises integrating the focal plane array into an infrared camera.
 17. The method of claim 13, wherein the forming of the leg structure further comprises forming first portions of a second layer on the portions of the first layer, wherein the leg structure further comprises the first portions of the second layer.
 18. The method of claim 17, wherein the forming of the leg structure further comprises: depositing the first layer on portions of the sacrificial layer; performing a spacer etch of the first layer so that the portions of the first layer remain on the sidewalls; depositing the second layer over the portions of the first layer on the sidewalls, over the bolometer bridge structure and, over the contact structure of the device; depositing a third layer over the second layer; and removing second portions of the second layer and portions of the third layer, wherein the second portions of the second layer are removed such that the first portions are on the portions of the first layer.
 19. The method of claim 17, wherein the first portions of the second layer have a first dimension that extends in the first direction and a second dimension that extends in the second direction, wherein the first dimension of the first portions of the second layer is greater than the second dimension of the first portions of the second layer, and wherein the portions of the first layer and the first portions of the second layer are adjacent to each other and stacked in a direction along the plane.
 20. The method of claim 17, wherein the forming of the leg structure further comprises: forming portions of a third layer on the first portions of the second layer, wherein the leg structure further comprises the portions of the third layer, wherein the portions of the first layer are on a first side of the first portions of the second layer, wherein the portions of the third layer are on a second side of the first portions of the second layer, and wherein the first side is opposite the second side. 